The first influx had clearly arrived from Alaska, as some of them still bore traces of their breeding plumage. On September 15 there were And today? The likely maximum summer population is about , but whatever the final number, at any given time there are hundreds of the creatures on the land or in the air, constantly moving about and mingling with one another: how can he possibly tell how many there are?
They can be found every summer, says Massey University ornithologist Phil Battley, congregating in northern harbours like Kaipara, Manukau and Kawhia; the Firth of Thames is another popular spot, as is Farewell Spit. Their total New Zealand population is currently estimated to be about 80, For centuries, birdwatchers have relied on banding in order to find out where migratory birds go.
Even today, an elaborate system of different-coloured bands and flags attached to birds continues to provide critical information about migration patterns. But it obviously cannot tell us what the birds are up to during their flights, nor how long it takes them to get from point A to point B.
For that, ornithologists are relying increasingly on satellite telemetry. Last year, several godwits summering over in the Firth of Thames were equipped with transmitters before they left for the north. Thanks to this technology, it has been confirmed that the bar-tailed godwit Limosa lapponica baueri flies non-stop further than any other bird in the world. In a Proceedings of the Royal Society paper, Gill, Battley and eight other authors state that in a female godwit unceremoniously named E7 flew 11, km from Alaska to New Zealand without stopping, easily exceeding the previous official record of km, flown by far eastern curlews.
Researchers had hoped at best to track her northward migration and maybe just a bit of the trip back. This year, however, only two of five transmitters worked all the way up to Alaska, and none at all worked for the return trip. And now there are no more plans to do further transmitter work, as funding provided by the Packard Foundation for godwit research has run out. In any case, he adds, no matter how smart the satellite technology, the battery aspect is always going to be problematic.
The survey has revealed two other remarkable aspects to the flight of the godwits. Nor do we know why they leave when they do.
Can they somehow sense when the meteorological moment is right? If so, what effect will major climate change have on them? According to Gill, the greater threat is the projected changes in both the frequency and the intensity of the storms that come across the north Pacific, the storms that produce the winds that get these godwits started on their migration.
Stunning stuff. Through studying them so closely and for so long, presumably Gill has grown very fond of godwits. More by Denis Welch. More by Neil Fitzgerald. Unlimited access to every NZGeo story ever written and hundreds of hours of natural history documentaries on all your devices. Signed in as. Sign out. Lost your password? Create an account. Ask your librarian to subscribe to this service next year. Related items. In flight uniform colour and pattern, wing stripe often indistinct; feet partly project beyond tail.
In breeding plumage most males undergo a complete transformation, becoming bright rufous on the head, neck, breast and belly, with strongly contrasting upperparts — dark feathers with buff fringes and notches. Females are considerably less colourful, becoming strongly streaked and barred on neck, breast and flanks, sometimes with pale rufous wash.
Juveniles that have recently arrived in New Zealand are recognisable by the broader buff margins to their scapular and back feathers, making them appear more mottled than adults; this plumage is rapidly moulted and replaced. Voice: godwits most commonly call in flight, usually a-wik,a-wik,a-wik. For most of their time in New Zealand they are usually silent on the ground, but immediately before migration departures there is a notable increase in both frequency and volume of calls from individuals that are about to leave.
Similar species: black-tailed godwit and Hudsonian godwit are both smoother grey-brown on the back, have prominent white-and-black wingbars, and a white rump contrasting with their black tail. The bill is slightly upturned in Hudsonian godwit, but is straight in black-tailed godwit. Whimbrels are slightly darker, with striped heads and down-curved bills. Eastern bar-tailed godwits breed in western Alaska and migrate to New Zealand and eastern Australia.
They are widely distributed around the country and some birds may occur on almost any harbour or estuary, although the bulk of the population occur at larger sites: Parengarenga, Kaipara, Manukau, Firth of Thames, and Farewell Spit. Bar-tailed godwits predominantly forage on soft intertidal substrates but may also be found probing in wet pasture. The population of subspecies baueri eastern bar-tailed godwit is likely less than , birds, 75, of which occur in New Zealand. Bar-tailed godwits are fully protected in New Zealand.
Godwits tend to be wary and easily spooked, and so preventing or minimising disturbance at high tide roost sites is an important conservation consideration. As with other migratory species using the East Asian Australasian Flyway, bar-tailed godwits face a real and potent threat from habitat loss, particularly at critical migration stopover sites in the Yellow Sea region. They are subjected to subsistence harvest by indigenous people in Alaska, but the number of birds taken is probably minimal.
Predicted Global Climate Change is likely to affect birds at all stages of their annual cycle. Expansion of shrubs and trees into tundra regions is likely to reduce suitable breeding habitat. Earlier peak invertebrate emergence in response to temperature changes may lead to major disruption of breeding strategy: that is, peak food supply may have occurred before hatching.
Utilising suitable wind patterns is a key component of godwit migration strategies, so changes to synoptic weather patterns on migration routes is likely to pose major problems for these birds. Rising sea levels will greatly reduce intertidal foraging habitat at wintering, staging and post-breeding sites. The conservation status of this species was changed to At Risk, Declining in Eastern bar-tailed godwits breed on upland and coastal tundra on the western rim of Alaska, from the coast to up to km inland, from the Gulf of Alaska to North Slope.
A clutch of four eggs is laid in a shallow bowl often lined with lichen. The pay-off for these huge eggs is fully developed and mobile chicks at hatching.
Parents share incubation and brooding post-hatching, but one parent may depart for the migration staging area earlier. Young fledge after days. Juveniles arrive in New Zealand after their first trans-Pacific flight when barely four months old. Bar-tailed godwits forage over the intertidal zone at low tide — either individually dispersed or in loose formations.
They congregate in flocks at high tide roosts, but can be extremely wary birds, often difficult to closely approach at New Zealand sites. In parts of Auckland, flocks are commonly seen commuting between the Manukau and Waitemata Harbours. Migration departures are staggered through March, in flocks varying between less than ten birds to over a hundred.
Individual birds have their own departure schedule and will aim to leave within the same day window each year. Snow cover which clears in southern areas from early May but not until the beginning of June in the north explains these staggered departures. Post-breeding adults and juvenile birds congregate along the southern coast of the Alaskan Yukon-Kuskokwim Delta preparing for southward migration.
Birds tracked by satellite on their 11,, km flights to New Zealand took days, with an average flight speed of 56 kph. They also forage in wet pasture for terrestrial invertebrates. On breeding grounds, they consume cranefly larvae and other invertebrates, and some berries, particularly soon after arrival. Battley, P. Journal of Avian Biology 43 : Conklin, J. Impacts of wind upon rigid individual migration schedules of New Zealand bar-tailed godwits.
They leave in groups. Structurally, they have a wing shape designed for fast, efficient long-distance flight. Their feathers are very sleek so that the wind can pass over as smoothly as possible.
The birds also counteract wind resistance drag by flying in flocks. The benefit of flying in a flock is that they fly in a V-formation. This means the bird at the front cuts into the wind first so that there is less wind resistance for the other birds. This makes flying easier for them, and as a result, the whole flock benefits by not becoming so exhausted.
The birds have turns at taking the lead because the lead bird encounters the most drag and has to work the hardest. During the flight, they use up the fat they have stored plus some of their muscle tissue, which increases before the flight to cope with their extra weight. In his PhD research, Jesse explored the relationship between when godwits leave New Zealand and when they return.
It appears groups of godwits return to New Zealand in the same order as when they left. Jesse discovered that migration timing is linked to the breeding grounds in Alaska. The birds seem to know exactly when to leave, and they leave at much the same time every year. Alaska is frozen over for about 6 months of the year.
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